Created attachment 8512113[details][diff][review]
Changed popupset id=mainpopupset element from blist.xul DOM
Check out the patch I have submitted, and let me know if there are any problems in it.
Thanks,
Kapil

Comment on attachment 8512113[details][diff][review]
Changed popupset id=mainpopupset element from blist.xul DOM
Review of attachment 8512113[details][diff][review]:
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Thanks for the patch.
Obviously either replacing all the mainPopupSet with mainpopupset, or all the mainpopupset with mainPopupSet would work for Instantbird when using only the built-in overlays, but there may be existing add-ons that correctly used mainPopupSet; so I think in order to not break them we should change the id in the overlays, rather than in the windows.